Photo-electric positioning device

ABSTRACT

Photo-electric positioning device for adjustment to a very accurate position in the manufacture of micro-circuits in which the enlarged images of the three first reflecting references drawn on the object to the positioned are centered on second opaque reference marks engraved on a translucent plate, a modulator disk having two concentric tracks rotating on each side of the said opaque references transmitting an identification signal to photo-electric cells which automatically control the lateral displacement of the object to center correctly each image on the corresponding reference mark.

United StatI Bay/533G2 0 Benard July 4, 1972 [54] PHOTO-ELECTRICPOSITIONING 3,457,422 7/1969 Rottmann ..250/219 DR DEVICE [72] Inventor:Christian Louis Georges Benard, Paris, Primary Exammer Archle BorcheltFrance Attorney-Karl W. Flocks [73] Assignee: Societe Parisienne desAnciens Etablisse- 57 ABSTRACT ments Barbier, Benard 8: Turenne, Paris,France Photo-electric ositionin device for ad'ustment to a very ac- 1...cura e position In t e manu acture o mlcro-clrcults m w lc [22] May261970 the enlarged images of the three first reflecting references [2|Appl. No.: 40,681 drawn on the object to the positioned are centered onsecond opaque reference marks engraved on a translucent plate, a [52] U8 Cl 250/208 356/172 modulator disk having two concentric tracksrotating on each 51 nl't'clffffffffffffffl'"" IIIIIIIIIIIIII .1161,-39/12 Side of Said Opaque references transmitting identifies 58 Field ofSearch ..250/208, 201, 203, 219 1); Signal to Photo-electric cells whichautomatically comm 3 56/172 the lateral displacement of the ob ect tocenter correctly each image on the corresponding reference mark. [56] IReferences Cited UNITED STATES PATENTS 10 Claims, 5 Drawing Figures3,207,904 9/1965 Heinz 3 56/l 72 PHOTOELECTRIC 37- 30 CELLS 29 I I, IPHOTOELECTRIC '1 CELL i MOTOR l 26 I l 34 33 32 & 1' f arm r J 1RESPONSE -fv i 7 clngun p 0 POSITIONING 1 l j I l IEJ ,5 9 l .LIGHTLIGHT SOURCE J g l l I i I I l l 1 I BACKGROUND OF THE INVENTION Thepresent invention relates to a photo-electric positioning device, andmore particularly to a device comprising photoelectric cells, amodulator disc and an optical unit permitting an adjustment having aprecision which is independent of the accuracy of the respectivepositions of the cells, of the light sources and to a certain extent ofthe centering of the modulator disc.

The adjustment to a very accurate position, for example to within a fewmicrons, in a definite emplacement, of an object movable parallel to afixed plane is advantageously effected in numerous applications,especially in the case of cutting out in the manufacture ofmicro-circuits and in numerous machining operations in micro-mechanicalwork, in which it is necessary to place a piece with great precisionwith respect to a tool in order to carry out subsequent machining,cutting and like operations. For this purpose, there are frequentlyemployed telescopes aimed in thefirst place on appropriate referencemarks on a typical piece occupying the desired position and then on theother pieces which are to be brought into the same position. Thissolution necessitates aiming operations which are slow, tiring for theoperator's eyes, and subject to human error.

For these reasons, the invention proposes to replace direct sighting byphoto-electric servo-control, by means for example of three lenses infront of which three photo-electric cells, replacing the eye of theobserver, control from a distance a mechanism which automatically andrapidly carries out the desired aiming operations. However, in orderthat photo-electric positioning, the bulk of which, it should be noted,is larger than that of simple sighting telescopes, may give the desiredresults, it is necessary that the lenses should maintain invariablerelative positions with a tolerance less than the final error permittedfor the accuracy of the desired position. The relative localization towithin a few microns of three electronic devices cannot be obtained bysimply placing them in position, the more so when the piece to besighted is of such small size that it becomes necessary to elbow theoptical channels, of which only the lenses can be placed side by sidedirectly above the reference marks of the object to' be sighted.

SUMMARY OF THE INVENTION The present invention has therefore for itsobject a photoelectric servo-control device which is free from thedisadvantages referred to. Its essential characteristic feature residesin the fact that each'of several lenses supplies an image of a firstreference mark drawn on the piece for its accurate positioning. Thisimage is formed in a plane on which a second reference mark has beenprovided, having a position intended to be at the center of the saidimage enlarged, the said second reference mark being preferably drawn ona first transparent plate or on sheets of glass stuck on this plate, thesaid first plate being invariably associated with a second opaque platefixed to the lenses.

The photo-electric cells corresponding to each reference mark give anerror signal which is a function of the lack of coincidence of eachreference, and remotely control the mechanisms which bring the piece tobe adjusted into the correct position.

The invention also provides an indeformable optical unit and a modulatorreading device of high precision.

BRIEF DESCRIPTION OF THE INVENTION invention;

FIG. 2 is a plan view taken along the line lI-II of FIG. 1;

FIG. 3 is a plan view of the modulator device, taken along the lineIII-III of FIG. 1;

FIG. 4 is a view with parts broken away of an alternative form of FIG.1;

FIG. 5 is a detail view of an alternative form of the modulator deviceof FIG.3.

DESCRIPTION OF THE PREFERRED EMBODIMENT S There can be seen from FIGS. 1and 2 an object 1 to be sighted, on which have been drawn three firstreference marks 2, 3 and 4, for example in the form of a reflectingdeposit of aluminum. The remote-control enables the object 1 to be movedparallel to its plane with three degrees of freedom indicated on FIG. 2by the lateral arrows f and f, and the rotational arrow f2, about thepoint 0. I The object 1 is previously placed with an approximateadjustment in such manner that the reference marks 2, 3 and 4 aresubstantially presented in the optical planes respectively of the lenses5, 6 and 7.

The lenses 5, 6 and 7 are inset in a plate 8 rigidly fixed to a cylinder9 closed at its upper portion (seeFIG. l) by a translucent ortransparent plate 10.

On the translucent or transparent plate 10 there have been providedthree second reference marks ll, 12 and 13, which are for example opaquelines drawn on the plate itself or on small plates 14 stuck on the plate10. 7

Three rhombohedral prisms 15, 16 and 17 are stuck beneath the plate 10in such manner as to transfer respectively on to the second opaquereference marks 11, 12 and 13, the images of the first references 2, 3and 4.

The optical unit jointly and severally enclosing the lenses 5, 6 and 7and the prisms 1.5, 16 and 17 rigidly fixed to the plates 8 and 10, thelatter plate bearing the opaque references 11, 12 and 13, is animportant feature of the invention.

It can be seen that if light sources 18, and 20 and a third one notshown are provided opposite orifices 21 formed in the cylinder 9, eachof the first reference marks 2', 3 and 4 can be illuminated by means oflenses 22 and parallel-face sheets 23. These reference marks beingprovided in the form of reflecting marks of aluminum, can give throughthe lenses 5, 6 and 7, the sheets 23 and the prisms 15, 16 and 17,images (not shown) which are substantially centered on the second opaquereference marks 11, 12 and 13 provided above the plate 10 the essentialpurpose of which will be explained later.

There is provided above the plate 10 a modulator disc 24 supported on ashaft 25 driven by a motor 26, of the synchronous type, for example.

On the disc 24 are engraved two concentric tracks 27 and 28 which arealternately transparent and opaque and displaced by a half-period withrespect to each other, as shown in FIG. 3. The circle separating the twotracks is arranged substantially so as to pass through the opaquereferences 11, 12 and 13 at which the images are formed, enlarged forexample six times by the lenses 5, 6 and 7, of the reference marks 2, 3and 4. If the first references 2, 3 and 4 are lines of the same size asthe opaque lines of the second references ll, 12 and 13, it can be seenthat the images extend widely on each side of the opaque lines.

Each of the tracks 27 and 28 filtersthe light signal emitted by theseimages in the form of square periodic signals.

The signals thus emitted by the reflecting lines 2, 3 and 4 arerespectively received by the photo cells 29, 30 and 31 through therespective focussing lenses 32, 33 and 34.

By means of three photo-electric servo-control response circuits andpositioning means such as that shown diagrammatically at 35, the cellsactuate displacements in the form of a positive, negative or null actionin one direction or the other indicated by the double arrows f f andthis latter rotation being effected in response to the differencebetween the signals received by the cells 29 and 31.

In fact, it is only necessary that the image centered on each opaquereference mark such as 11 is displaced in one direction or in the otherfor the periodic square light signals transmitted by one and the othertrack to differ in amplitude, and that it resultson the photo-electriccells in an order signal, the sign of which may be identified withrespect to a reference phase in a manner known per se.

The tracks of FIG.3 are provided with three periods per revolution, butthere may advantageously be provided two tracks 27' and 28' such asthose shown in FIG. 5, with one period per revolution in order toassociate the identification with the supply to the synchronous motor.

The function of the second opaque reference marks is especially todefine a neutral zone covering as widely as may be desired the centeringerror of the circle separating the two tracks of the modulator disc,this error being associated with the assembly of the mechanism ofrotation of the disc 24 driven by the shaft 25, the accuracy of whichcan only be technically ensured in a very approximate manner.

It is seen that the sensitivity of the response of the cells 29, 30 and31 is solely associated with the indeformability of the fixed opticalunit 8, 9, 10, the relative positions of the light sources of the lenses22, the plates 23, the modulator disc 24, the lenses 32 and the cellsbeing capable of being chosen with relatively large tolerances,

At the level of the position reference mark of the object, the inventionthus provides a precision of 2 microns which, in view of themagnification (six for example) of the lenses 5, 6, and 7, necessitatesan accuracy of reading of 12 microns at the level of the plate 10,whereas the precision which can theoretically be expected at this levelof a servo-control device according to the invention, is actually 2microns.

FlG.4 is a view of an alternative form in which the illumination iseffected by means of a light source 18' through the disc 24, and theseperiodic square signals are received on a cell 29 through the orifice21, which has the advantage of removing the sources of heat 26 and 18'from proximity of the optical unit 8, 9, 10.

It will be understood that the present invention has been describedabove by way of a simple indication of a preferred example and not inany limitative sense, and that any equivalents may be introduced in itsconstituent elements without thereby departing from its scope as definedby the appended claims.

What is claimed is: 1

l. A method of high precision optical positioning, characterized in thatit comprises the following steps: illuminating a first reflectingreference mark drawn on the object to be adjusted; receiving theenlarged image of this latter reference on a second opaque referencemark drawn on a transparent plate; causing the passage on each side ofthe said image centered on the said second reference, of two tracks on amodulator disc alternately opaque and transparent and displaced by ahalfperiod; reading in the form of periodic square optical signals thelateral displacement of the image with respect to its centered position;identifying the sense of the displacement on a photo-electric cell inthe form of a positive, negative or neutral signal; and controlling thedisplacement of the object to be adjusted so that the image of the firstreference is correctly centered.

2. A method in accordance with claim 1, characterized in that threefirst reference marks are provided on the object to be positioned andthree second opaque reference marks on the periphery of the transparentplate, the images of the said first references being projected on to thesecond references by means of rhombohedral prisms secured to the saidplate.

3. A method in accordance with claim 2, characterized in that threelenses intended to give the said images of the first references areinset in an opaque plate rigidly coupled to the said transparent plate.

4. A method in accordance with claim 1, characterized in that the saidfirst reference marks are produced by an aluminide deposit.

5. A device for high precision positioning of an object, characterizedin that it comprises an object positioning means to move the objectparallel to a fixed plane with three degrees of freedom of movement,three remote-control photoelectric cells, each controlling a movement ofsaid positioning means in one degree of freedom in response to a squareoptical signal, an optical unit transmitting three images of three firstreflecting references drawn on the object to be positioned disposed onsaid positioning means and including a plate allowing the passage oflight therethrough on which are engraved three second opaque referencemarks, the said images being centered on the said second opaquereferences, a modulator disc having two concentric tracks rotating oneach side of the said opaque references transmitting an identificationsignal to the said cells.

6. A device in accordance with claim 5, characterized in that saidoptical unit comprises said light passing plate on which is engraved atleast one opaque mark, and further including at least one rhombohedralprism stuck on said plate, an opaque plate in which is inserted at leastone magnifying lens, the light passing plate and the opaque plate beingrigidly coupled together by means of a mounting cylinder pierced withopenings.

7. A device in accordance with claim 6, characterized in that sources oflight illuminate said first references through said openings, each cellreceiving the square optical signals transmitted by the modulator discdirectly through a lens.

8. A device in accordance with claim 6, characterized in that sources oflight directly illuminate said modulator disc through a lens, each cellreceiving the optical signals through one of the said openings.

9. A device in accordance with claim 5, characterized in that twodisplacements of said freedom of movement are movements of translationat each actuated by one of said cells, the third displacement being arotation in response to the difference between the signals from said twocells.

10. An optical unit characterized in that it comprises a transfer plateon which is engraved at least one opaque mark, at least one rhombohedralprism secured to the said plate, an opaque plate in which is inserted atleast one magnifying lens, the transfer plate and the opaque plate beingrigidly coupled together by means of a mounting cylinder pierced withopenings and a modulator disc in the path of light to said transferplate.

UNITED STATES PATENT OFFICE. CERTIFICATE OF CORRECTION Patent No. 3 ,675,024 Dated July 4, 1972 I Invent fls) Christian Louis Georges Benard Itis certified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

In column 1, after line 9, the following claim for priority should beinserted:

May 27, 1969 France 6917215 Signed and sealed this 12th day of'Deoember1972.

(SEAL) Attest:

EDWARD M.FLETCHER,J'R. ROBERT GO-TTSCHALK Attesting Officer Commissionerof Patents FORM PO-105(1O'59) USCOMM-DC 60376-P69 a T5, GOVERNMENTPRINTING OFFlCEI I969 0-366-33fl

1. A method of high precision optical positioning, characterized in thatit comprises the following steps: illuminating a first reflectingreference mark drawn on the object to be adjusted; receiving theenlarged image of this latter reference on a second opaque referencemark drawn on a transparent plate; causing the passage on each side ofthe said image centered on the said second reference, of two tracks on amodulator disc alternately opaque and transparent and displaced by ahalf-period; reading in the form of periodic square optical signals thelAteral displacement of the image with respect to its centered position;identifying the sense of the displacement on a photo-electric cell inthe form of a positive, negative or neutral signal; and controlling thedisplacement of the object to be adjusted so that the image of the firstreference is correctly centered.
 2. A method in accordance with claim 1,characterized in that three first reference marks are provided on theobject to be positioned and three second opaque reference marks on theperiphery of the transparent plate, the images of the said firstreferences being projected on to the second references by means ofrhombohedral prisms secured to the said plate.
 3. A method in accordancewith claim 2, characterized in that three lenses intended to give thesaid images of the first references are inset in an opaque plate rigidlycoupled to the said transparent plate.
 4. A method in accordance withclaim 1, characterized in that the said first reference marks areproduced by an aluminide deposit.
 5. A device for high precisionpositioning of an object, characterized in that it comprises an objectpositioning means to move the object parallel to a fixed plane withthree degrees of freedom of movement, three remote-control photoelectriccells, each controlling a movement of said positioning means in onedegree of freedom in response to a square optical signal, an opticalunit transmitting three images of three first reflecting referencesdrawn on the object to be positioned disposed on said positioning meansand including a plate allowing the passage of light therethrough onwhich are engraved three second opaque reference marks, the said imagesbeing centered on the said second opaque references, a modulator dischaving two concentric tracks rotating on each side of the said opaquereferences transmitting an identification signal to the said cells.
 6. Adevice in accordance with claim 5, characterized in that said opticalunit comprises said light passing plate on which is engraved at leastone opaque mark, and further including at least one rhombohedral prismstuck on said plate, an opaque plate in which is inserted at least onemagnifying lens, the light passing plate and the opaque plate beingrigidly coupled together by means of a mounting cylinder pierced withopenings.
 7. A device in accordance with claim 6, characterized in thatsources of light illuminate said first references through said openings,each cell receiving the square optical signals transmitted by themodulator disc directly through a lens.
 8. A device in accordance withclaim 6, characterized in that sources of light directly illuminate saidmodulator disc through a lens, each cell receiving the optical signalsthrough one of the said openings.
 9. A device in accordance with claim5, characterized in that two displacements of said freedom of movementare movements of translation at 90*, each actuated by one of said cells,the third displacement being a rotation in response to the differencebetween the signals from said two cells.
 10. An optical unitcharacterized in that it comprises a transfer plate on which is engravedat least one opaque mark, at least one rhombohedral prism secured to thesaid plate, an opaque plate in which is inserted at least one magnifyinglens, the transfer plate and the opaque plate being rigidly coupledtogether by means of a mounting cylinder pierced with openings and amodulator disc in the path of light to said transfer plate.